Acrylonitrile-butadiene rubber, also referred to herein as NBR, is an established article of commerce which is prepared by the copolymerization of acrylonitrile with butadiene and, optionally, a minor amount of isoprene.
The hydrogenation of acrylonitrile-butadiene rubber is well know. Processes to hydrogenate NBR are described in U.S. Pat. Nos. 4,384,081, 4,581,417, and 4,503,196, the disclosures of which are incorporated herein by reference. Partially hydrogenated acrylonitrile-butadiene rubber typically exhibits improved resistance to heat aging in comparison to unsaturated acrylonitrile-butadiene rubber.
Processes to halogenate polymers are also known. However, the reaction of a halogen with rubber frequently results in the formation of an adduct having a high fraction of insoluble material (i.e., "gel"). Although gelled polymers are useful in certain applications, particularly in adhesives, gel is normally considered undesirable because it causes difficulty in compounding and mixing processes. Furthermore, attempts to vulcanize gelled rubber normally provide vulcanizates with poor tensile strength and elongation at break properties.
I have discovered useful adducts of a partially hydrogenated NBR and a halogen selected from bromine and chlorine. Preferred adducts of the present invention are characterized by having a surprisingly low gel level of less than 10%, as measured by weight % insoluble after 16 hours in methyl ethyl ketone (MEK) at 30.degree. C.
It is an object of the present invention to provide an adduct of a partially hydrogenated acrylonitrile-butadiene rubber and a halogen selected from bromine and chlorine.
It is another object of the present invention to provide a process to prepare an adduct of a halogen and a partially hydrogenated acrylonitrile-butadiene rubber.
It is a further object of the present invention to provide a vulcanizate prepared by curing a low gel adduct of a halogen and a partially hydrogenated acrylonitrile-butadiene rubber.